The prior art contains many bone distraction devices which permit bone lengthening by cutting the bone and distracting the ends of a bone apart by a desired distance, affixing the ends in place with a permanent or temporary internal splint and filling the gap between the bone ends with a bone segment to facilitate growth across the gap. Devices of this type are disclosed in U.S. Pat. Nos. 4,929,247 to Rayhack; 3,244,170; 3,604,414; 4,475,546; 4,187,841; 3,709,219; and 2,333,033.
Most of the foregoing distraction devices do not provide for gradual distraction of the bones. In fact, most of these devices permit bone distraction only for the purpose of inserting a bone segment in the gap between the distracted bone ends. These devices then compress the bone sections to prevent the bone segment inserted therebetween from falling or slipping out the gap.
U.S. Pat. Nos. 4,096,857 to Kramer, et al., and 3,976,060 to Hildebrant, et al. disclose implantable distraction devices which permit gradual bone distraction between osteotomically separated bone sections. The Hildebrant patent discloses a number of devices having sealed housings, each of which has an extension means and power drive means for extending the extension means to distract separated bone sections. Hildebrant further discloses that the power drive means may be controlled by a control means such as electronic control circuitry which may be actuated externally by a magnetic field located outside the device's housing, even outside the patient's body.
Notwithstanding the achievements of the prior art devices, a need still exists for an implantable distraction device which provides or is capable of the following: (1) providing gradual distraction between osteotomically separated bone sections, (2) easily implanted and attached to a patient's osteotomically separated bone sections, (3) has an extremely low profile so that it is not easily detected even though it may be subcutaneously located just under the skin, (4) economically constructed using a minimal number of parts, and (5) structurally stable when anchored to bone so that the occurrence of flexural moments is minimized between the device's points of attachment to the osteotomically separated bone sections.